CCD and CMOS
Oct 1, 2008 12:00 PM, By Steve Mullen
Understand old and new camera sensor technology.
Figure 9. Frame accumulation defines total photodiode integration time as a multiple of the current interframe interval. This image was shot using 16-frame accumulation.
CMOS sensors typically offer a maximum exposure time of one-fiftieth or one-sixtieth second. To obtain greater sensitivity, as is done with CCDs, video gain can be increased. When even greater sensitivity is required, some CMOS cameras offer the option to specify a number of accumulated frames. Frame accumulation defines total photodiode integration time as a multiple of the current interframe interval.
CMOS accumulated modes do not suffer from increased image noise, but can have significant blur on moving objects. The image in Figure 9 was shot using 16-frame accumulation.
Figure 10. This image was shot with a Sony HVR-V1 using its +36dB hyper gain option.
CCDs typically obtain super high sensitivity by engaging hyper gain. The result is a significant increase in image noise. Motion, however, remains clear. (See Figure 10.)
These high sensitivity modes are quite different and support different shooting goals.
Forecast
Both CCD and CMOS sensors will be used for years to come. Moreover, both technologies will employ multiple implementation strategies to meet performance goals and price points.
Steve Mullen is owner of Digital Video Consulting, which provides consulting services and publishes a series of books on digital video technology.
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